[9.18] fix: dev: Fix memory ordering issues with atomic operations in the quota.c...

[9.18] fix: dev: Fix memory ordering issues with atomic operations in the quota.c module

Change all the non-locked operations on `quota->used` and
`quota->waiting` to "acq/rel" for inter-thread synchronization. Some
loads are left as "relaxed", because they are under a locked mutex
which also provides protection.

Also use relaxed memory ordering for `quota->max` and `quota->soft`,
as done in the main branch; possible ordering issues for these
variables are acceptable.

Closes #5018

Merge branch '5018-quota-memory-ordering-fixes-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!10203